The invention relates to compositions, methods, and apparatuses for improving the performance of primary settlers and washer circuits for red mud in a Bayer Process. As described for example in U.S. Pat. Nos. 6,814,873, 6,033,579, 6,048,463, and US Published Patent Application 2008/0257827, in the Bayer Process alumina trihydrate is extracted from bauxite ore. Bauxite ore is pulverized then goes through a digestion stage (where it is slurried in a caustic liquor medium and is heated under pressure), a clarification stage, a precipitation stage, a classification stage, and finally a calcination stage from which the final product is recovered.
In the clarification stage red mud is separated from the alumina in the ore. Red mud is the large percentage of the ore that remains insoluble after digestion with caustic medium. This insoluble traction must be removed prior to the alumina trihydrate recovery step in the process so as to avoid contaminating the final Bayer Process product. The digestion slurry consists of finely suspended mud particles which are commonly removed by the addition of flocculants in large separation vessels called thickeners or settlers. The flocculant acts to bind the mud particles increasing their rate of settling in the thickener. The overflow liquor then typically reports to filters, often referred to as Security Filtration, to remove any remaining insoluble material prior to alumina trihydrate recovery. The red mud slurry from the thickener underflow contains valuable alumina and caustic in solution that is recovered in the Red Mud Washer Circuit otherwise known as a counter-current decantation (CCD) circuit. Over several stages, mud slurry is mixed with progressively more dilute (lower in valuable alumina and caustic) wash water. The advancing wash water progressively increases in caustic and alumina content as it recovers the valuables from the mud slurry, then ultimately exits as a dilution stream for use back into the process at an appropriate point. The resulting red mud is sent to disposal. Some examples of red mud clarification are described in U.S. Pat. Nos. 3,085,853, 3,397,953, 3,445,187, 3,541,009, 3,681,012, 4,767,540, and 5,008,089.
Because of the cost associated with each additional filtration and dilution step, large savings and efficiencies can be realized from reducing the number or intensity of the required filtration and dilution steps. As a result, there is clear utility in novel methods of more effectively flocculating and separating red mud from the red mud-containing liquors.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 CFR§1.56(a) exists.